The present invention relates generally to filters for liquids, and more particularly, to the construction of a liquid flow filter wherein, by reason of the construction and arrangement of its components, the filter will not clog or become blocked during operation. By way of background, a principal advantage for a filter made according to the principles of the present invention is that two distinct liquid flow paths are provided, and three separate mechanisms are at work during operation of the filter.
One principal application of the filter of the invention is that of cleaning solvent used in washing mechanical parts, particularly auto, truck, and like mechanical parts that have become oily, greasy or otherwise require cleaning before reinstallation, rebuilding, or repair of the parts or a mechanism of which they form a component.
In many cases, cleaning solvent for mechanical parts is retained in the sump or reservoir of a large square tank or cylinder drum and circulated by means of a pump from the sump of the tank or drum to a cleaning area, often a sink or the like, and then allowed to flow by gravity back into the receptacle. As the solvent picks up the dirt from the work being cleaned, it entrains particulate matter and becomes dirty and discolored rather quickly. While a certain amount and kind of contaminants will inherently be separated from the body of the solvent in the reservoir merely by settling or sedimentation, because of the agitation caused by the circulation itself, or the pump action, and because of the relatively small particle size of such contaminants, it is quite common for the solvent being used in such a cleaning operation to require frequent changing.
In the past, attempts to filter such solvent for cleaning purposes have had two or more principal drawbacks. One typical drawback with such an arrangement is that when filter comprises simply a screen, or a loose mass of absorptive material, such material is not effective to separately dispersed, fine contaminants. Such a filter may act to remove coarse materials, but is not particularly effective against relatively fine contaminants.
To the extent that such filters are made from a finer mesh or less porous material, such as utilizing a paper cone or other type construction, the filters, after a relatively brief time, have their working surfaces coated with a layer of the contaminants. This impedes rapid flow through the filter, effectively slowing or reducing the treatment rate to an undesirable level. Moreover, retaining a significant volume of fluid in a location above the unit center of gravity can create at least a slight safety hazard. Accordingly, most parts washers have typically used relatively course or crude filter arrangements.
In other instances, attempts have been made to secure good filtration action by using a relatively fine mesh filter. Examples of this approach include using automotive type oil filters or the like that are themselves capable of removing relatively fine contaminants. However, filters of this kind typically have two inherently associated drawbacks.
First, such filters often require a relatively strong force to cause fluid flow; this is attributable to their fine mesh size. While such characteristic is satisfactory in an automotive lubrication application, for example, where the oil circulation system is powerful, this is not a consideration with a parts washer which uses a small, fractional horsepower motor and which requires most or all of the pumping effort merely to circulate the solvent to a height of several feet above liquid level. In such instances, there is no ready reserve of power available to supply the motive force necessary to force the liquid through the filter at a satisfactory rate.
Another aspect of any fine mesh filter, including automotive filters, that are capable of filtering out small particles, is that they can become clogged, i.e., they become impermeable when the interstices in the filter are filled with entrapped contaminants. In most instances, a bypass mode is provided for this contingency. However, this requires the maintenance of a significant forward pressure level, i.e., a measurable force is required to unseat a check valve or the like. If this is not the case, then the filter would operate exclusively in the bypass mode and not be effective. Hence, such bypass arrangements have traditionally been associated only with filters used in higher pressure systems.
Referring now to problems peculiar to the parts washer industry, in many instances, it is desired, for reasons of legal and regulatory compliance, to provide an established, properly permitted company to service solvent-containing parts washers. In some instances, the servicing agency is the owner of the machine, and more or less regular service intervals may be honored. However, in the case of a customer owning a parts washer, problems have traditionally arisen. First, it is desirable that it be made clear to the customer in a clear and straightforward way when a change of solvent is indicated.
Thus, although changing solvent on a regular schedule has some advantages. Some customers feel it is wasteful to change solvent too often, but they realize that failure to change soon enough degrades solvent performance and creates a number of risks. Consequently, they often desire to wait until the solvent is dirty and then call in for a change of solvent. This may take some time, and users do not wish to risk failure in the time between calling for service and the time the service is performed.
Because of the presence of the aforesaid regulations and the like, it is therefore not uncommon for customers to fail to change solvents with the regularity that should be required. Attempts by users to change their own filters or replace solvents themselves often run afoul of regulatory requirements.
Accordingly, it would be considered very advantageous if there were available a solvent filter system which would greatly simplify service of parts washers in the field.
It would likewise be very advantageous for a number of parts washer users if there were readily available a parts washer filter unit that would continue to deliver substantially unimpeded flow of solvent, even after the effective service life of the filter had diminished almost completely.
It would also be considered very advantageous if there were available a solvent filter for a parts washer wherein observing the solvent could be made to provide an accurate indication of the amount of residual contaminants in the solvent and wherein the parts washer operation could be continued to and beyond a normal end point without significant damage without significantly compromising the solvent flow rate.
In view of the foregoing circumstances, including the failure of the prior art to provide an improved, highly advantageous filter system for a parts washer, it is an object of the present invention to provide an improved liquid filter unit.
Another object of the invention is to provide a solvent filter that is capable of continuing to supply solvent to a parts washer outlet at a substantial flow rate, regardless of the extent to which the filter removing the contaminants has accumulated contaminating material.
Still another object of the invention is to provide an improved modular solvent filter assembly for parts washers or other uses wherein the filter assembly is designed for ready insertion into and removal from an exterior protective housing.
A further object of the invention is to provide a filter arrangement including an exterior, liquid-tight bag, receptacle or container within which is disposed a sleeve made from porous material and arranged in a labyrinth within the housing, and wherein the sleeve has an inlet, and both the sleeve and the receptacle have outlets for the liquid passing through the filter.
A still further object of the invention is to provide a filter assembly that includes a porous filter element constructed and arranged so as to provide inlet and outlet openings, and having permeable sidewalls, with such filter element being disposed inside a pouch or bag type receptacle that is impermeable to fluid, and wherein, in use, liquid passes into and out of the filter element interior, and also through the walls of the element, and wherein fluid thereafter flows from both the filter interior element outlet opening and the bag interior as well.
Yet another object of the invention is to provide a filter assembly having two interior spaces, one space being an inner space lying within a non-woven fabric or like filter element and the other space lying outside the filter element but within an exterior receptacle, preferably having flexible walls, with passages being provided so as to permit fluid to flow both into and out of the inner space and also outwardly of the unit as a whole from the outer space between the filter element and the exterior container.
A further object is to provide a filter which is substantially non-clogging in use and that inherently provides a substantially continuous bypass mode of operation.
Another object of the invention is to provide a filter assembly having an exterior, liquid-impermeable outer container that may be rigid or flexible, and wherein a sleevelike filter element of great length relative to its cross-section is contained inside this outer container to provide both an inner space for unfiltered liquid and an outer space for liquid that has been filtered but remains inside the outer container.
Yet another object of the invention is to provide a filter assembly which may be economically manufactured and which may be used as a unit or may be used in modular form in conjunction with one or more additional, substantially similar units to achieve longer life in use or increased filter capacity.
A further object of the invention is to provide a filter unit wherein the filter element, preferably in sleeve or tube form, is made from a permeable fabric, such as from fine non-woven plastic fibers or like material with the sleeve or tube having open inlet and outlet ends spaced well apart from each other, and arranged so that the long tube thus formed provides a large, active filter area and has a substantial interior volume.
A still further object of the invention is to provide a filter assembly having an inner filter element made from a porous, fine mesh material in tube, sleeve or like form and disposed within a liquid-impermeable outer container having flexible sidewalls, with the elements being arranged so that, when the pump is turned off, the expanding forces on the flexible outer sidewalls will be relaxed, and the walls will contract and cause filtered fluid to flow back into the area inside the filter element so as to create a backwashing or self-cleaning action within the filter assembly.
Another object of the invention is to provide a filter arrangement wherein one or more novel filter elements are used in connection with an exterior protective cabinet and a manifold or like flow-directing arrangement whereby a single stream of solvent or like liquid may be directed from an inlet to and through various passages and emerge as a single stream or as separate streams for use at the point of application.
A further object of the invention is to provide a novel filter assembly which is particularly useful in parts washing apparatus and the like.
A still further object of the invention is to provide a filter assembly having a mechanism that is particularly effective when operated at comparatively low flow rates and under minimal pressures.
Another object of the invention is to provide a filter assembly which inherently provides both filtration and bypass modes, and wherein the proportion of fluid that is filtered to that which is unfiltered is largely or completely self-regulating in use.
Yet another object of the invention is to provide a non-clogging filter which may be arranged to provide a visible warning of its filtration effectiveness.
A further object of the invention is to provide a filter that is able to be manufactured at low cost and will be highly reliable in use.
A still further object of the invention is to provide a method of filtering liquids which includes passing a part of such liquid through a filter element and permitting the remainder of the filter to entrap contaminants on the filter walls or to separate from the fluid by sedimentation, whereby the remainder of the liquid will emerge in a cleaned but unfiltered condition.
Yet another object of the invention is to provide a method of filtering liquids which includes passing a portion of the liquid to be treated through a filter element and permitting the remainder to flow unfiltered throughout an extended length within a space on the interior of the element, and utilizing both outlet streams in a cleaning, lubricating, or cooling process.
An additional object of the invention is to provide a method of liquid filtration which is operable at low flow rates and at extremely low pressures.
Another object of the invention is to provide a filter assembly wherein the filtration effectiveness and service life of the unit may be determined readily and comparatively accurately by visual observation.
A further object is to provide a filter element which includes a shape-imparting element, such as a tube or pipe from a sponge or foam-like material, covered on its exterior with a fine mesh, non-woven fabric material.
A still further object is to provide a filter element made from opposed sheets of a non-woven fabric material, heat sealed together along a selected seaming path to provide a labyrinth or similar shape having a high length to cross-section ratio.
Yet another object is to provide a filter element as set forth above, used in combination with an exterior, flexible-walled receptacle that includes inlets and outlets sufficient to provide both bypass and filtration modes in use.
A further object of the invention is to provide a filter assembly whose operational mechanism renders it compatible with either rigid or flexible filter elements, and with either rigid and flexible exterior containers.
The foregoing and other objects and advantages of the invention are achieved in practice by providing a filter assembly having an exterior, fluid-impermeable container receptacle with at least one outlet opening, a filter element made from a porous material and having an interior passage space extending between inlet and outlet openings and being disposed inside the exterior receptacle so as to create an exterior space between the container and the filter, whereby unfiltered liquid passes through the inlet and into and through the interior passage and to the filter element outlet, and wherein liquid also passes from the inlet, through the walls of the filter element and into the outer space, and thereafter through the receptacle outlet to the point of use. Preferably, the filter assembly includes fittings adapted to direct the fluid into and out of the respective inner and outer spaces provided by the filter element and the exterior container, and to simplify attachment and replacement of the filter assembly. The invention provides construction features making it easy to arrange the filter assemblies in pairs or other multiples, and a method of cleaning solvent.
The exact manner in which the foregoing and other objects and advantages of the invention are achieved in practice will become more clearly apparent when reference is made to the following detailed description of the preferred embodiments of the inventions set forth by way of example and shown in the accompanying drawings, wherein like reference numbers indicate corresponding parts throughout.